1. Field of the Invention
Embodiments of the invention generally relate to initiators for detonating explosives or igniting flammable solids. More particularly, embodiments of the invention relate to non-explosive initiators for use with downhole tools requiring initiation to detonate explosives or ignite flammable solids therein.
2. Description of the Related Art
Forming a hydrocarbon well typically begins by drilling a borehole from the earth's surface to a selected depth in order to intersect a hydrocarbon bearing formation. Steel casing typically lines the borehole formed in the earth. This creates an annular area between the casing and the borehole that is filled with cement to further support and form the wellbore.
Various drilling and completion operations utilize tools having explosives or flammable solids therein that must be either detonated or ignited at a desired time and location in the wellbore. For example, one type of radial cutting torch uses a flammable solid to produce a high velocity jet that pyrotechnically cuts tubing located in the wellbore. This ability to cut tubing downhole becomes necessary when a tubular string becomes stuck in the wellbore and requires removal in order to continue operations. In another example, perforating guns typically use radially oriented shaped charges that are connected by a detonating cord and detonated at a predetermined depth in the wellbore to form perforations in the casing, the cement and/or the formation. The perforations caused by the firing of the shaped charges enable and/or enhance production at that location in the wellbore.
Initiators detonate or ignite the explosives or flammable solids, which are known as secondary loads, disposed in the tools by first initiating a primary load within the initiator that then initiates the secondary load. Past initiators include a low energy initiator that utilizes an electronic controller with lead wires connected to a bridgewire that only needs to be heated to the ignition temperature of the primary load of a primary explosive such as lead azide next to the bridgewire. Radio frequency (RF) sources and stray voltages found on well sites and offshore platforms from devices such as radio transmitters, electric welders, and cathodic protection equipment must be turned off in order to prevent the lead wires from acting as an antennae and supplying a current which could cause premature and potentially catastrophic initiation of the tool. Thus, going “radio silent” when non-radio-safe initiators are used interrupts valuable work time at the rig and effects incoming helicopter flights trying to locate the rig and data communication systems between the rig and shore that monitor and control various rig systems remotely.
More recently, the tools requiring initiation employ radio safe initiators using an exploding bridgewire (EBW) or an exploding foil initiator (EFI) to initiate a material, such as a secondary explosive, that is less thermally sensitive than a primary explosive used in past initiators. With the EBW, a large amount of energy is applied very rapidly into a thin bridgewire such that the current heats the wire through the melting, boiling and vaporization phases to provide an explosion that gives off thermal energy and a shock wave used to initiate the primary load of the initiator. Regarding the EFI, a large amount of energy is applied very rapidly into a thin metal foil which vaporizes to cause a flyer material to accelerate toward and impact the primary load of the initiator such that the primary load is initiated. In contrast to the low energy initiators of the past, the initiators with the EBW and the EFI require additional electronic circuitry such as capacitors to reach a high energy threshold required for functioning. The threshold can be approximately 200 kilowatts and 200 amperes. Thus, these high thresholds make the initiators with the EBW and the EFI immune from stray voltages and less susceptible to accidental initiation.
While current initiators are safer, they are still classified as explosives, which require special shipping, storage and handling. One type of initiator device utilizes an EBW in combination with a flammable solid that includes a mixture of ferrous oxide and aluminum, known as thermite. This combination requires that the initiator device be classified and regulated as an explosive device.
Furthermore, obtaining explosive licenses in international locations requires increasingly more lead time and is becoming more complex. Thus, the initiator must be shipped on more costly non-passenger flights and meet other handling requirements even though some of the tools that the initiator is being used with are not classified as explosives. Accordingly, the classification of the initiator as an explosive increases costs and time required to get the initiators to the site of the rig.
Thus, there exists a need for initiators that are radio safe, shippable by standard air freight, otherwise safe to handle and ship and do not require explosive permits and licenses. A further need exists for initiators for use with downhole tools, particularly those tools that utilize flammable solids.